I happen to be one of those people that carry an MP3 player everywhere (I listen to books), so this would actually be a convergence device for me, and I'd at least consider buying one.
I do worry about the quality and reliability however. Seems like a monumental challenge to design quality and reliability into two devices at once, especially since they are inherently non-compatible (heat, liquid, electronics). I can see why it's taking so long since concept, and I'll bet you'll overshoot your estimates by another year. And I'll place another bet that you won't recover your investment.